This invention relates to the field of optics and lasers, and more specifically to a method and apparatus including multi-compositional glass substrates and related devices and optical waveguides on a glass substrate.
The telecommunications industry commonly uses optical fibers to transmit large amounts of data in a short time. One common light source for optical-fiber communications systems is a laser formed using erbium-doped glass. One such system uses erbium-doped glass fibers, or a small slab substrate of erbium-doped glass having waveguides formed on or near one face of the substrate, to form a laser that emits at a wavelength of about 1.536 micrometer and which is pumped by an infrared source operating at a wavelength of about 0.98 micrometer, such as a semiconductor laser diode. One method usable for forming waveguides in a substrate is described in U.S. Pat. No. 5,080,503 issued Jan. 14, 1992 to Najafi et al., which is hereby incorporated by reference. A phosphate glass useful in lasers is described in U.S. Pat. No. 5,334,559 issued Aug. 2, 1994 to Joseph S. Hayden, which is also hereby incorporated by reference. An integrated optic laser is described in U.S. Pat. No. 5,491,708 issued Feb. 13, 1996 to Malone et al., which is also hereby incorporated by reference.
To increase signal-carrying bandwidth, an optical fiber can carry a plurality of different wavelengths (i.e., colors), wherein each wavelength is modulated (e.g., using amplitude modulation) with a different signal stream. Dense wavelength-division multiplexing (DWDM) is the name for one such scheme wherein each signal stream is modulated on a carrier wavelength that is close to, but slightly different than, the neighboring wavelengths. For example, the carrier wavelengths can be chosen in the infrared at, say, 1536 nm, 1536.8 nm, 1537.6 nm, etc., for a wavelength spacing of 0.8 nm per channel. Many such wavelengths/channels can be combined and transmitted on a single optical fiber. Since photons have extraordinarily low or no interaction with one another, these channels are transmitted with no crosstalk or other inter-channel interference. Further, a broadband light amplifier can be used to simultaneously amplify all the colors/channels by equal amounts, also without introducing crosstalk. The challenge, thus, is to be able to separate the channels (i.e., to split off each channel""s color without also getting interfering light signals from adjacent channels"" colors).
It is desirable to be able, at, for example, a building in downtown Minneapolis, to extract one channel from the plurality of optical channels of data carried on a single optical fiber, e.g., to extract a first data stream that is modulated on the 1536.8 nm channel from all the other channels on some single optical fiber, and to insert in its place a second data stream that is modulated on the 1536.8 nm channel. The remaining channels being transmitted on the optical fiber should be undisturbed. This allows data that has a destination in that building to be separated and delivered into that building, and for other data in the second data stream to be sourced from that building and sent elsewhere.
There is a need in the art for an integrated optical system, including one or more high-powered lasers and/or amplifiers, along with routing and other components, that can be inexpensively mass-produced. The system should be highly reproducible, accurate, and stable. In particular, there is a need for an amplifier with stable and high gain formed on a relatively small glass substrate. There is further a need to having improved delivery of pump light to the active waveguides. There is further a need for improved add-drop devices that permit extraction of a first signal stream at a first wavelength from a plurality of other signal wavelengths, and insertion of a second signal stream modulated onto a laser carrier of the first wavelength.
The present invention is embodied by a amplifier, laser, and/or other optical, or combined, waveguide component that is formed using a glass substrate. In some embodiments, some or all portions of the substrate are doped with one or more optically active lanthanide species. The integrated optical device has one or more of waveguides defined by channels within the substrate.
One aspect of the present invention provides an integrated photonic apparatus that includes a glass substrate having a major surface, a plurality of waveguide segments on the surface of the substrate including a first waveguide segment and a second waveguide segment, and a folded evanescent coupler connecting the first waveguide segment to the second waveguide segment. In some embodiments, the folded evanescent coupler includes an evanescent coupler formed by a length portion, having a first length, of the first waveguide segment and an equivalent length portion of the second waveguide running parallel and adjacent to the length portion of the first waveguide segment, wherein the first length is substantially equal to one half of an evanescent coupler length needed to transfer a first wavelength in a non-folded evanescent coupler, and a reflector located at an end of the folded evanescent coupler.
In some embodiments, the first length is a length selected to transfer substantially all light of a first wavelength from the first waveguide segment to the second waveguide segment.
In some such embodiments, the reflector is a dielectric mirror that is highly reflective to light of the first wavelength. In some such embodiments, the reflector is also highly transmissive to light of a second wavelength, wherein the first wavelength is different than the second wavelength.
In some embodiments, the integrated photonic apparatus also includes a first port configured to launch signal light into the first waveguide segment, a second port configured to launch signal light into the second waveguide segment, and a third port configured to launch signal light into both the first waveguide segment and port configured to launch signal light into the first waveguide segment and into the second waveguide segment. In some such embodiments, the third port is through the reflector.
In some embodiments, the first length is a length selected to transfer substantially all light of a first wavelength from the first waveguide segment to the second waveguide segment, while the length is also selected to transfer substantially no light of a second wavelength from the first waveguide segment to the second waveguide segment, wherein the first wavelength is different than the second wavelength.
In some embodiments, the first length is a length selected to transfer substantially all light of a first wavelength from the first waveguide segment to the second waveguide segment, while the length is also selected to transfer substantially all of a second wavelength from the first waveguide segment to the second a waveguide segment, wherein the first wavelength is substantially different than the second wavelength.
Another aspect of the present invention provides an integrated photonic apparatus including a glass substrate having a major surface, a plurality of waveguide segments on the surface of the substrate including a first waveguide segment, a second waveguide segment, a third waveguide segment, a fourth waveguide segment, a first folded evanescent coupler connecting the first waveguide segment to the second waveguide segment, and a second folded evanescent coupler connecting the third waveguide segment to the fourth waveguide segment.
In some embodiments, the first folded evanescent coupler includes an evanescent coupler formed by a length portion, having a first length, of the first waveguide segment and an equivalent length portion of the second waveguide running parallel and adjacent to the length portion of the first waveguide segment, wherein the first length is substantially equal to one-half of an evanescent coupler length needed to transfer a first wavelength in a non-folded evanescent coupler, and a first reflector located at an end of the first folded evanescent coupler. In some embodiments, the second folded evanescent coupler includes an evanescent coupler formed by a length portion, having a second length, of the third waveguide segment and an equivalent length portion of the fourth waveguide running parallel and adjacent to the length portion of the third waveguide segment, wherein the second length is substantially equal to one half of an evanescent coupler length needed to transfer a second wavelength across a non-folded evanescent coupler, and a second reflector located at an end of the second folded evanescent coupler.
The present invention also provides apparatus and methods for amplifying light in a relatively short transverse distance on a glass substrate. Various embodiments include combinations and sub-combinations of the described subdevices, functions, and/or features.